docs: def commit_log(self, log_json):
          """ Commits a run log to the Mongo backend.
  
          Due to limitations of maximum document size in Mongo,
          stdout and stderr logs are truncated to a maximum size for
          each task.
          """
  
          log_json['_id'] = log_json['log_id']
          append = {'save_date': datetime.utcnow()}
  
          for task_name, values in log_json.get('tasks', {}).items():
              for key, size in TRUNCATE_LOG_SIZES_CHAR.iteritems():
                  if isinstance(values.get(key, None), str):
                      if len(values[key]) > size:
                          values[key] = '\n'.join([values[key][:size/2],
                                                   'DAGOBAH STREAM SPLIT',
                                                   values[key][-1 * (size/2):]])
          self.log_coll.save(dict(log_json.items() + append.items()))